258 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 8 



Period of Activity 



Since the first parasitized chinch bug eggs were found on Msiy 6 it 

 is evident that the parasites were active before this date. The first 

 chinch bug eggs were found on May 5. 



The last emergence of parasites in the life history study in the out- 

 door insectary under practically natural conditions occurred October 

 21 and the last parasite died November 30. The period from the first 

 parasitism in the spring to the last emergence in the fall was 168 days' 

 and to the last death 209 days. 



Number of Generations 



The possible number of broods was determined in an outdoor in- 

 sectary by collecting parasitized chinch bug eggs as soon as they ap- 

 peared in the field in the spring and rearing adult parasites. The adults 

 were allowed to oviposit in chinch bug eggs immediately and in this 

 way the next generation was obtained. By supplying the first adults 

 of each generation with fresh chinch bug eggs an unbroken life history 

 record for the entire summer was obtained. The first brood of adults 

 was present in the field prior to May 6 as parasitized eggs were found 

 at this date. The second brood of adults was bred from eggs on May 

 27, the third brood was out June 11, the fourth brood June 28, the 

 fifth brood July 15, the sixth brood Juh^ 31, the seventh brood August 

 15, the eighth brood September 1, and the ninth brood September 24. 

 The first pair of adults of the ninth generation was supplied with 17 

 chinch bug eggs and oviposition occurred at once. The larvae of this 

 brood, however, died just before pupation. The accompanying chart 

 gives the seasonal life histt)ry and brood study at Manhattan. 



Physiological Relations 



Effect of Temperature. — Eiimicrosoma henefica responds readily 

 to temperature influences. Low temperatures of from 40° to 50° pro- 

 long the life cycle from sixteen daj^s to forty-two or more days and 

 prolong the length of adult life from three to ten days to as high as 

 seveiity-eight days. On July 13 several parasitized eggs w^ere placed 

 in an ice box where the temperature ranged between 42° F. and 55° F. 

 One egg was removed each w^eek and the time of emergence was pro- 

 longed just the period that the eggs remained in cold storage. The 

 parasite that w^as in cold storage seven days emerged seven daj^s later 

 ' than the check, and the parasite that was in tvv'enty-nine daj^s emerged 

 tw^enty-nine days later than normal. 



On August 8 eighty-four parasites were fed on sweetened water and 

 placed in an ice box where the temperature ranged between 40° F. and 



